Previous attempts at designing hub-mounted vehicle motion sensors have included hub-mounted vehicle backup alarms and hubodometers. For example, an attempt at a hub-mounted vehicle backup alarm design is the subject of U.S. Pat. No. 5,132,665 of Hutchisson et al. Attempts at electronic versions of hubodometer designs are the subjects of U.S. Pat. No. 4,989,222 of Lutts et al. and U.S. Pat. Nos. 6,940,940 and 8,352,210 of Kranz. These previous attempts can be loosely categorized according to designs relying on moving parts (e.g., as in the '665 and '222 patents) and designs lacking moving parts (e.g., as in the '940 and '210 patents).
The previous designs relying on moving parts have employed multiple magnetic-field (e.g., reed or Hall effect) sensors for detecting a magnetic field that varies as a function of wheel rotation. These designs needed two or more such sensors, despite the added cost and complexity, in an attempt to discriminate between forward and reverse motion or to reject effects of spurious motion caused by transient forward and reverse rocking of a wheel. Furthermore, these prior attempts were relatively inefficient at generating electrical power because they were direct-drive systems in which a generator rotated only once per each wheel rotation.
The previous designs lacking moving parts afforded no means by which to produce electrical energy for powering internal electrical circuitry. For that reason, these systems have depended on batteries that must be manually replaced when depleted. Also, these systems use one or more accelerometers to detect motion, but the accelerometers cannot readily distinguish between rotational motion and irrelevant (vibratory) motion. To address this issue, some designs have included complicated signal-processing filter techniques or have used multiple (i.e., redundant) accelerometer signals in attempting to distinguish between meaningful signals representing a wheel rotation and irrelevant signals representing spurious motion.